Sick JP-8..help needed

[Philip]

hi all,

A freind sent me this. I am not familiar with the JP-8. Any suggestions?
All are welcome.
Philip

> BTW, I'm not
> sure how familiar you are with the Jupiter 8, but I figured that you might
> know something about it since you plan on doing some Jupiter 6 mods. Somebody
> I know is having some problems with his JP8. He just got it back from a tech
> who had it for 6 months or a year or something and he still couldn't fix the
> problem. It is as follows:
> 
> VCO 1 on Voice A is drifting eractically. Due to the analog nature, all the
> VCOs drift a little, but there is a discinct problem with this particular VCO.
> The best way to describe it is, let's say I tune VCO 1 and 2 to unison so
> there is no beating. Well VCO 1 will stay stable for a few seconds, then
> suddenly drift so you will hear beating between the oscillators(major beating)
> and then will come back in line every so often. There is no pattern or logic
> to this behavior. The tech I took it to said he thinks there is some kind of
> noise being introduced into the VCO 1 circuit causing this unstability, but he
> does not know how to get rid of it. He replaced all of the following chips
> surrounding this circuit:
> 
> CA3046
> R9A
> R12
> R10
> IC1A,3A
> TR1A
> TLO81 chip
> 4558 chip
> 25A1015
> 
> Even after all this the problem still exists. Anything that can get this
> keyboard going again would be awesome. I really miss playing it.




-- 
Philip Pilgrim                  The Lab Audio Works
5 Evan's Drive                  - Analog/Digital Recording/Processing
Hammonds Plains                 - Computer/Synth Interfacing
Nova Scotia, Canada             - Hardware/Software Development
B4B 1M8

Phone     +1.902.835.7844
Email      mailto:thelab at sprint.ca

Web Page: http://www.robotnik.com/the_lab